The ban has been put in place "to provide a safe environment for law enforcement activities."

According to the FAA notice, relief aircraft operations "under direction of St. Louis County Police Department" are allowed in the airspace, and commercial planes landing and leaving from the St. Louis Lambert Airport are exempt.

There are several slightly conflicting reports on why the police department requested the temporary flight restriction. A police department spokesman told Brian Ries of Mashable that the decision was made after a police helicopter came under fire on Sunday:

Spox: "That decision was made immediately when our police helicopter came under fire Sunday night, due to hostile scene..."

A St. Louis County Police Department helicopter dispatcher (who only identified himself as "Chris") told Think Progress the no-fly zone was put in place because the department was having trouble with news teams. “It’s just for a no fly zone because we have multiple helicopters maneuvering in the area and we were having some problems with news aircrafts flying around there,” he said.

FAA spokesman Tony Molinaro told BuzzFeed that the police department asked for the ban to keep the area clear of low flying aircraft that obstructs police work. “It’s not an unusual request by law enforcement agencies, especially when they’re trying to get any of their aircraft in and out of an area,” Molinaro said.

News reports are focusing on the Germanwings pilot's possible depression, following a familiar script in the wake of mass killings. But the evidence shows violence is extremely rare among the mentally ill.